Measurements of Magnetic Field Distributions With an Optically Pumped K-Rb Hybrid Atomic Magnetometer

We have developed a K-Rb hybrid optically pumped atomic magnetometer (OPAM) for biomagnetic measurements. With this hybrid OPAM, we used a linear photodiode array and a charge-coupled device (CCD) sensor to instantaneously measure 1-D and 2-D magnetic field distributions generated by a test coil, respectively. The measured distributions were compared with those calculated using the Biot-Savart law and showed good agreement for the linear photodiode array; however, in the case of the CCD sensor in the area away from the test coil, the intensity of the detected magnetic field was slightly different from the calculated one, possibly because of the diffusion of the spin-polarized atoms as well as smear and blooming in the CCD sensor. The sensitivity of the OPAM was 5-6 pT/Hz^1/2 using the linear photodiode array and ~10 pT/Hz^1/2 using the CCD sensor. In future experiments, we plan to fabricate a sensor cell with a high density of probe atoms and reduce the noise generated in the electronic circuitry of the detectors in order to increase sensitivity.